no they are not.
but
>The fact that I'm calling a function, it must exist, otherwise the compiler will throw an error ("undefined reference to function")
you mean the linker will throw an error. The linker is trying to link together the "references" be they forward or backward, that the compiler has created, and the compiler needs to have generated the right references, round peg round hole, square peg square hole.
You don't want your linker throwing errors, it doesn't have the context the compiler does; and you don't want to turn the linker into ChatGPT that can converse with you about your source code, just use the C version of forward references which are not particularly forward, they just say "I don't know where this is defined, it's just not defined here, but we know it's a square peg"
For example, there are architectures where space is tight (embedded for example) and nearby things can be called more efficiently than far away things, so the compiler needs to generate as many near calls as it can, falling back to far away when it has to. It doesn't know in advance how far away things are going to be, but it might uncover plenty of near things as it goes. Square pegs, round pegs.
when you recompile your project code, the library code, is not necessarily around. When other people recompile their library code, your project code isn't around. What's the size of what's being put on the stack? Still gotta get the square/round pegs right.
